Echinococcus

Source: Wikipedia, the free encyclopedia.
This article is about the organism. For the infection, see Echinococcosis.

Echinococcus
Necropsy of a cotton rat infected with Echinococcus multilocularis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Family: Taeniidae
Genus: Echinococcus
Rudolphi, 1801
schematic representation of the life cycle of Echinococcus
General description of the egg and oncosphere of Echinococcus spp.

Echinococcus is a genus within Cestoda, a parasitic class of the platyhelminthes phylum (colloquially known as flatworms). Human echinococcosis is an infectious disease caused by the following species: E. granulosus, E. multilocularis, E. vogeli[1][2] or E. oligarthrus.[2]

Echinococcus is triploblastic – it has three layers – outermost

proglottids
. Its body shape is ribbon-like.

In humans, Echinococcus spp. cause a disease called

alveolar echinococcosis caused by E. multilocularis, and polycystic echinococcosis caused by E. vogeli or E. oligarthrus.[3] A worm's incubation period is usually long and can be up to 50 years. Cystic echinococcosis is mostly found in South and Central America, Africa, the Middle East, China, Italy, Spain, Greece, Russia, and the western United States (Arizona, New Mexico, and California
).

Echinococcosis is a

intermediate hosts
are infected by ingesting eggs. Sheep, goats, cattle, camels, pigs, wild herbivores, and rodents are the usual intermediate hosts, but humans can also be infected. Humans are dead-end hosts, since their corpses are nowadays seldom eaten by carnivorous predators.

The egg hatches in the digestive system of the intermediate host, producing a planula larva. It penetrates the intestinal wall and is carried by bloodstream to liver, lung, brain, or another organ. It settles there and turns into a bladder-like structure called

hydatid cyst
. From the inner lining of its wall, protoscoleces (i.e. scoleces with invaginated tissue layers) bud and protrude into the fluid filling the cyst.

After the death of the normal intermediate host, its body can be eaten by carnivores suitable as definitive hosts. In their small intestines, protoscoleces turn inside out, attach, and give rise to adult tapeworms, completing the lifecycle. In humans, the cysts persist and grow for years. They are regularly found in the liver (and every possible organ: spleen, kidney, bone, brain, tongue and skin) and are asymptomatic until their growing size produces symptoms or are accidentally discovered. Disruption of the cysts (spontaneous or

iatrogenic e.g. liver biopsy
) can be life-threatening due to anaphylactic shock.

Cysts are detected with ultrasound,

indirect fluorescent antibody, complement fixation, ELISA, Western blot, and other methods.[4]

Taxonomy

A phylogenetic tree has been created for several species in this genus – Echinococcus oligarthrus, Echinococcus vogeli, Echinococcus multilocularis, Echinococcus shiquicus, Echinococcus equinus, Echinococcus ortleppi, and Echinococcus granulosus.[5] The first diverging species are the neotropical endemic species E. oligarthrus and E. vogeli. E. ortleppi and E. canadensis are sister species, as are E. multilocularis and E. shiquicus. E. canadensis is related to E. granulosus.

The origin of these parasites based on host-parasite co-evolution comparisons was North America or Asia, depending on whether the ancestral definitive hosts were

felids
.

Echinococcus oligarthrus and Echinococcus vogeli are basal in this genus.

Taenia from which it diverged more than 10 million years ago. The genus Echinococcus evolved in North America in canids and began to diversify 5.8
 million years ago.

In 2020, an international effort of scientists from 16 countries lead to a detailed consensus on terminology, i.e. the terms to be used or rejected for the genetics, epidemiology, biology, immunology and clinical aspects linked with Echinococcus species.[7]

Prevention

There is no vaccine against Echinococcus multilocularis. However, it is possible to protect humans from the fox tapeworm by deworming the main hosts.[8][self-published source]

References

  1. ^ Dandan, Imad (7 May 2019). "Hydatid Cysts". Medscape. Retrieved 24 November 2023.
  2. ^ a b "Echinococcosis". DPDx - Laboratory Identification of Parasites of Public Health Concern. Centers for Disease Control and Prevention. 15 July 2019. Retrieved 24 November 2023.
  3. ISBN 92-9044-522-X
    . Retrieved 24 November 2023 – via World Health Organization.
  4. PMID 22235225
    .
  5. S2CID 42494141
    .
  6. PMID 21907295
    .
  7. PMID 32500855. Article No. 41. Open access icon
  8. ^ Grabs A (November 2016). How To Exterminate The Fox Tapeworm In Your Area – via Amazon Kindle Store.
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